Spherical titanium sublimator

ABSTRACT

A sublimator is described for subliming a material such as titanium. The sublimator comprises a generally spherical hollow body of the material to be sublimated enclosing a source of heating energy. The wall of the hollow body is uniformly thick over its full extent, and the configuration of the heat source is correlated to the inner surface of the spherical body to provide a generally uniform rate of total heat energy absorption at substantially all portions of the body. The result is that the body sublimates uniformly from its full outer surface, and at the time in which any one portion of the body is fully dissipated, i.e., when an aperture appears through the body, the remaining portion of the body is also substantially dissipated.

United States Patent Harra 51 May 9, 1972 SPHERICAL TITANIUM SUBLIMATOR Inventor: David J. Hnrra, Palo Alto, Calif.

Assignee: Varian Associates, Palo Alto, Calif.

Filed: Oct. 19, 1970 Appl. No.: 81,982

References Cited UNITED STATES PATENTS Hamilton ..4 1 7/49 Primary Examiner-C. L. Albritton Attorney-Stanley Z. Cole and Leon F. Herbert [57] ABSTRACT A sublimator is described for subliming a material such as titanium. The sublimator comprises a generally spherical hollow body of the material to be sublimated enclosing a source of heating energy. The wall of the hollow body is uniformly thick over its full extent, and the configuration of the heat source is correlated to the inner surface of the spherical body to provide a generally uniform rate of total heat energy absorption at substantially all portions of the body. The result is that the body sublimates uniformly from its full outer surface, and at the time in which any one portion of the body is fully dissipated, i.e., when an aperture appears through the body, the remaining portion of the body is also substantially dissipated.

18 Claims, 3 Drawing Figures This invention relates to sublimation devices and, more particularly, to such a device making increased utilization of the heat energy provided to cause the desired sublimation of a material, and which is so designed that the amount of available material which is actually sublimated is maximized.

It is often desirable to be able to provide in an initially evacuated environment a controlled atmosphere of a material in gaseous form. For example, thin film devices, such as microelectronic components and circuits, are commonly made by depositing a thin film of a desired material onto a substrate from a gaseous atmosphere formed from the material to be deposited. Also, in high vacuum pumping, condensation of a gettering material from an atmosphere of thematerial onto a gettering surface is used to constantly renew the gettering surface as well as provide mechanical burial of pumped particles.

The gaseous atmosphere of the material is quite often provided by sublimating the material. That is, a surface of a'body of a desired material is heated to the sublimation temperature of the material'to cause the solid material at the surface to pass directly to the gas phase without going through the liquid phase. Sublimation is preferred over evaporation from the liquid phase since it is much easier to support a solid in a vacuum chamber rather than a liquid, and sublimation is not limited to formation of the gas from only its upper surface as is evaporation from a liquid. However, presently available sublimation devices, or sublimators as devices of this nature are often called, suffer from certain disadvantages. For example, it is difficult to provide adequate rates of material sublimation without requiring complex apparatus. One approach taken by those in the art in an effort to obtain increased rates of sublimation is that of heating from the interior a cylinder of the material to be sublimed. The heat passes through the cylindrical wall of the body and causes sublimation of material from the full outer surface of the body, rather than just from a limited area. The increased sublimating area causes a cor responding increase in the amount of material sublimated in a given length of time. While cylindrical sublimators are now in use, they have several serious deficiencies. They do not, in general, make efficient utilization of the heat generated by the heat source. The heat is generally provided either by radiation or electron bombardment from a filament coaxially disposed .within the cylinder. Insofar as electron bombardment heating is concerned, the expense involved in providing the high voltage necessary to generate adequate and energetic electrons for acceptable heating rates has limited its acceptance. With most designs of radiation heating, a good portion of the heat energy is not utilized in heating the material. That is, much of the heat energy from a radiation source escapes from the ends of the cylinder, either directly or by reflection from the inner walls of the cylinder. The result has been that those in the art have turned to relatively complicated and expensive heating arrangements such as that disclosed in US Pat. No. 3,427,432.

Present designs of cylindrical sublimators have one other major problem. With most of such devices, there is generally a good portion of the getter material still in the solid state when the device burns out and thereby reaches the end of its life. That is, the midportion of a cylinder begins to sublime at a much faster rate than the end portions. This is because less heat can escape from the interior of the cylinder adjacent its midportion than can at its ends, and the ends of the cylinder generally have more surface area to radiate heat which would otherwise be effective for sublimation. Thus, when there is complete sublimation of material from a midportion thereof, i.e., when an aperture or hole forms through the cylinder, much of the material adjacent the ends of the cylinders is still in solid form. The formation of the hole at the center will enable escape of sufficient amount of heat that the power required to effectively sublimate the remainder of the material is too high to warrant the further sublimation. Thus, formation of the hole results in the end of the life of the sublimator even though a great proportion, sometimes as much as percent, of the material is still in solid form.

SUMMARY OF THE INVENTION The present invention provides a sublimation device which makes efficient use of all of the heat energy from a heat source, as well as assures that most of the material has been sublimated before the device becomes inoperative. The sublimator of the invention comprises a hollow body of a material to be sublimed having a source of heat energy located within its hollow portion. In keeping with a particularly salient aspect of the invention, the hollow body is substantially closed about the heat source so that heat energy flowing directly from the source as well as all heat energy reflected from the inner surface of the body, cannot escape from the body but rather must be absorbed by the material. Moreover, the inner surface of the body has a configuration assuring that heat energy reflected from any one portion of this surface is ultimately directed to another portion of the surfaceforabsorption by the material to be sublimed, thereby assuring full utilization of the heat energy.

It has beenfound that when the heat energy is fully utilized as above, one can suitably design the inner surface configuration and the configuration of the heat source relative to the wall thickness at all portions of the body so that the material becomes fully sublimed or dissipated from all portions of the body simultaneously. This means that when an aperture forms in the body to mark the end of the life of the sublimator, all other portions of the body also are substantially fully sublimed.

Most desirably, the wall of the body is of a generally uniform thickness and the configurations of the inner surface thereof and of the heat source are correlated to provide a generally uniform rate of total heat energy absorption at all portions of the body. This results in a uniform sublimation rate over substantially all portions of the outer surface of the body and simplifies the control of the total sublimation rate. It has been found that the simplest structure for providing the substantially closed hollow body and inner surface configuration relationship is a generally spherical hollow body having a uniformly thick wall. With such a structure, the inner surface of the body is also generally spherical in configuration and it has been found that the predominant amount of the total heat absorbed by any portion of such a configuration is heat energy which has been reflected from another portion of the surface, rather than heat energy which is directly radiated from the heat source. Thus, the particular configuration of the heat source becomes less critical than it is with other configurations.

BRIEF DESCRIPTION OF THE DRAWING With reference to the accompanying sheet of drawing:

FIG. 1 illustrates a preferred embodiment of the sublimator of the invention which is especially designed to sublimate a getter material and is incorporated into a vacuum system for high vacuum pumping;

FIG. 2 is an enlarged, mostly broken away view of the preferred embodiment of the sublimator illustrated in FIG. 1; and

FIG. 3 is a partial and broken away embodiment of an alternate embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The sublimation device of the instant invention is most useful in providing an atmosphere of a gettering material for condensation on surfaces within a vacuum system to aid in high vacuum pumping. For this reason, the sublimator of the invention will be described with respect to a preferred embodiment especially adapted for this purpose. With reference to FIG. 1, the sublimator, generally referred to by the reference numeral 11, is shown appropriately mounted within a vacuum system 12. System 12 includes an enclosure in the form of the bell jar 13 defining a high vacuum work environment. Bell jar 13 is mounted upon a base sump 14 to which a conventional diffusion pump system 16, including a roughing pump, is communicably connected. The sublimator ll of the invention is mounted within sump 14 with an electrical lead portion 17 thereof passing hermetically through the wall of the sump to the exterior. In operation, when electrical power is applied through lead portion 17 to the sublimator, gettering material sublimated therefrom forms a gaseous atmosphere within the sump 14 from which material condenses on the inner wall surfaces of the sump to thereby form gettering surfaces to aid in the high vacuum pumping. It will be appreciated that as is conventional a suitable baffle or valve can be provided between the sump 14 and the bell jar portion 13 to prevent any appreciable amount of the sublimated material from contaminating the bell jar environment.

Reference is now made to FIG. 2 for a more detailed description of the sublimator 11 of the invention. As is illustrated, the sublimator 11 includes a substantially closed, hollow body 18 made from the material to be sublimated. In the particular embodiment being described for use in high vacuum pumping, the material to be sublimated and from which body 18 is made is desirably titanium. As is illustrated, body 18 is generally spherical. That is, the body is made up of two, generally hemispherical body portions 19 and 21 which are suitably joined at their open ends such as by welding. It is to be noted that each of the body portions 19 and 21 is not a perfect hemisphere, but rather includes a short cylindrical or tubular section at its open end. When the two hemispherical portions are joined, the result is that the body is slightly elongated in the direction perpendicular to the hemispherical joining plane. For the purposes of this disclosure, though, the body including the relatively short tubular section joining the two perfect hemispherical sections, is referred to as generally spherical.

A source of heat energy is located within the hollow portion of body 18 to direct heat energy at the bodys inner surface 22 for conduction through the wall of the body to sublime material from the bodys exterior surface 23. More particularly, a helical filament 24 is supported within the body at one end by a molybdenum sleeve 26 which extends through the apex end of generally hemispherical member 19. The other end of filament 24 extends through a cylindrical aperture 27 in the apex end of generally hemispherical member 21 and is suitably connected to a electrical conductor rod 28.

The diameter of cylindrical aperture 27 should be sufficiently larger than the diameter of the filament end wire 29 passing therethrough that electrical breakdown between the wire and the aperture wall is prevented. However, the aperture should not be any larger than is necessary so that the loss of heat from the filament 24 through the aperture is minimized.

Support means, generally referred to by the reference numeral 31, are provided to facilitate mounting the body 18 within the sump 14. Such support means includes a support sleeve 32 which tightly receives in one end thereof a short cylindrical extension 33 projecting from the apex of hemispherical body portion 21. The other end of the sleeve 32 fits over a thicker walled tubular post 34 which is, in turn, received within a tubular acceptor rod 35. As is best illustrated in FIG. 1, tubular acceptor rod 35 is secured to a flange 36 which is hermetically sealed to another flange 37 welded to sump wall 38. It will be appreciated that any suitable hermetic sealing arrangement, such as the sealing flange configuration known by the registered trademark Conflat can be used to provide the desired hermetic seal.

The support means also includes means for mechanically supporting heater filament 24 in position, as well as delivering electrical power thereto. That is, end wire 29 of the heater filament extends coaxially into sleeve 32 where it is received into one end of connector rod 28. Conductor rod 28 has a necked-down portion 39 which is received within a cylindrical insulating plug 41 within post 34. It will be appreciated that plug 41 acts to mechanically support the full electrical lead structure for the filament as described to this point from the remainder of the support structure, while yet insulating the same therefrom. The free end of rod 39 is received within a female electrical connector 42 of the acceptor rod 35.

The tubular post 34 and lead portion 39 are removably received within the acceptor collar 35 and connector lead 42, respectively. Thus, when the sublimation unit 11 reaches the end of its life, a new sublimation unit can be substituted in its place, and the acceptor collar and flange arrangement used again.

For most efficient sublimation of material from the body 18 in accordance with the invention, the amount of heat loss because of the support structure should be minimized. To this end, the sleeve 32 is made as thin as it is practical to do so and yet assure that such sleeve has sufficient strength to support the body 18 at its high temperatures of operation. Moreover, a heat shield cup 43 coaxially surrounds the sleeve to minimize loss by radiation of heat from such sleeve. To further minimize the loss of heat from the body 13, a plurality of radiation shield discs 44 are held by an inner cylinder 46 secured to the end of post 34 at a location at which such discs minimize radiation losses from cylindrical section 33 of body 18. A suitable material for the various members of the support structure, except for the insulating plug 37, is molybenum. The insulating plug can be of any suitable ceramic.

As has been mentioned previously, as a particularly salient feature of the invention, it has been found that when a hollow body of gettering material such as body 18 is substantially closed so that substantially no heat energy from the source can escape, there is a relationship between the configurations of the inner surface of the body and the heat source, relative to the wall thickness of the body which can be used to maximize the total amount of material sublimated by the end of the sublimators useful life. That is, with such an arrangement, the rate of total heat energy absorption at each portion or segment of the body can be related to the thickness of the body at such portion to provide sublimation of all of the material at the end of a predetermined time interval. If the time interval is substantially the same for all portions of the body, the result is that all portions of the body are substantially dissipated at the time at which any one portion becomes dissipated. Thus, when the body of gettering material has reached the end of its life, i.e., when any portion of the wall of the body is so thin that it is incapable of supporting itself or when an aperture develops through the body, the material is also substantially dissipated from all other portions of the body. It will be appreciated by those skilled in the art that this correlation of the inner surface configuration and the configuration of the heat source to the wall thickness cannot be so critically determined to provide full dissipation of all of the material at the end of the predetermined time. Rather, because of various parameters which are not easily controlled, there is almost bound to be some material left at most portions of the body when a hole or aperture is about to develop at another portion. Thus, when it is referred to herein that all portions of the body are substantially dissipated" at the end of the life of the sublimator, it is meant that an appreciably greater amount of material is sublimated from the body than would be for a prior art structure, i.e., at least two or three times as much material.

In the preferred embodiment being described, the wall thickness of the body is generally uniform over its full extent. This feature has several advantages. For example, it simplifies the correlation of the bodys inner surface configuration to the configuration of the heater. That is, to provide the desired substantial sublimation of all portions of the body at the end of a predetermined time interval, it is only necessary to see that all portions receive the same rate of heating when the body is uniformly thick. The provision of the uniform thickness has the added advantage of assuring that the rate of sublimation of material is the same over the full area of the outer surface of the body. That is, there is no one portion of the outer surface of the body from which more material is being sublimated than at other portions. This is particularly helpful in use of the sublimator in high vacuum pumping since it means that gaseous material will be evolved from the body uniformly in all directions, thereby enabling renewal of various gettering surfaces within a vacuum system at generally the same rate.

With respect to the correlation of the configuration of the I heat energy source with that of the inner surface of the body, one would tend to think that in order to assure uniform heating of all portions of this surface, that the heater configuration would have to generally conform to that of the surface. That is, it would appear most reasonable that the outer envelope configuration of the heat source be also generally spherical or, in other words, have an outer configuration providing equal spacing of the heater from theinner surface of the body at all points. However, with many materials, it has been found when the body is substantially closed as described, the greater proportion of the heat energy actually absorbed by the material is not heat energy which comes directly from the heat source, but rather heat energy which has been reflected from the walls at some other portion of the body. For example, the emissivity of titanium is about 0.35. That means that only a little more than a third of the heat which is received at any one portion of the inner surface of the body is absorbed, the remainder being reflected. With a concavely curved and preferably hemispherical surface such as that described, the result is that reflection of heat from one portion to another accounts for a large portion of that heat actually absorbed by any segment of the body. Thus, the actual configuration of the heater, although important, becomes less critical. For this reason the generally helical wire arrangement shown, forming an open cylindrical heat radiating body, suffices to provide the correct configuration relationship.

Even though the support means 31 for supporting the body 18 is especially designed to minimize the amount of heat it conducts away from the body 18, it does act to some extent as a heat sink. As a particularly salient feature of the instant invention, the body includes means to compensate for the heat loss caused by the support means. To this end, the inner surface 22 of the body is roughened, such as by way of serrations, at 51, adjacent the location at which the support means is secured to the body. This roughening increases the absorption of heat at such portion. That is, because of the irregular surface, some of the heat energy which is reflected upon striking the body at this roughened portion will be directed toward another portion of the roughened surface, rather than away from the roughened portion such as to another location along the inner surface configuration. The result is that the total heat absorption rate of the body portion adjacent the roughened inner surface is greater than the other portions of the body surface. By varying the amount of roughness included, one can experimentally determine the amount of roughness necessary to assure that the added heat absorption adjacent the support means compensates for the heat loss caused due to the presence of the support means.

An experimental embodiment of the invention which was the same as the embodiment described above insofar as the body shape and heater configuration are concerned, had a 1.3 inch diameter at the plane joining the generally hemispherical sections 19 and 21. The body had a uniformly thick wall of 0.150 inches, thereby making the diameter of the body between the hemispherical apexes l.5 inches. The aperture 27 through which the heater wire 29 extended was 0.188 inches in diameter, and the total weight of getter material equaled 50.3 grams before sublimation, The filament heater 24 was made from about 17 inches of 0.032 diameter tungsten wire. The wire was wound in a helix having both a length and an outer diameter of about 0.65 inches.

In order to heat the outer surface of the body to a sublimation temperature of l,500 C, it was only necessary to apply to the heater filament 850 watts of power at 41 .7 amps. This lowpower requirement was due to the body being substantially closed and having a consequential low heat loss.

When the sublimator 11 had reached the end of its life, i.e., when the wall of the body had become so thin at one point it would not support its own weight, it was found that 30.8 of the original 50.3 grams had been dissipated. That is, approximately 61 percent of the material had been utilized. This should be contrasted to the 10 to 15 percent which is utilized in most conventional arrangements relying on internal heating of a body to cause sublimation.

It was found also that the rate of sublimation of the life of the body did not vary to any appreciable extent. This was attributed to the fact that during the life of the body the total surface area from which sublimation occurred did not appreciably vary. That is, the spherical geometry is the optimum closed geometry assuring that the decrease in size over the life of the body of the area of the surface from which material is sublimated is minimized.

While the spherical geometry and uniformly thick wall embodiment is preferred, it will be appreciated that the broad aspects of the invention can be realized with other configurations. FIG. 3 schematically depicts such another configuration. In the embodiment shown, the inner surface configuration 61 of the body of sublimable material 62 is generally cylindrical with conical end portions. When this inner surface configuration is combined with a helical heater filament providing an open cylindrical radiating surface as illustrated, a greater proportion of the heat energy from the filament will be absorbed by the gettering material adjacent its midportion than at its end portions. Thus, the body of gettering material is thicker at such location to compensate for the greater rate of sublimation thereat, so that all portions of the body will be fully sublimated at substantially the same interval of time as described above.

What is claimed is:

1. A source for providing sublimed material comprising a hollow body of a material to be sublimed, said hollow body having inner and outer surfaces, a source of heat energy located within said hollow body for directing heat energy at the inner surface of said hollow body for conduction through said body to sublime said material from said bodys outer surface, said hollow body being substantially closed to prevent escape therefrom of both the heat energy flowing directly from said source and the heat energy reflected from said inner surface of said body, the inner surface of said body having a configuration such that heat energy reflected from any one portion of said surface is ultimately directed to another portion of said surface for absorption by said material to be sublimated, said inner surface configuration and the configuration of said heat source being related to correlate the rate of total heat energy absorption at each portion of said body with the wall thickness at said portion so that substantially all of the material of said portion is sublimed at the end of a predetermined time interval which is generally the same for all portions of said body, whereby all portions of said body are substantially dissipated at the end of said interval to maximize the amount of material which is already sublimated from said body at the time at which any portion of said body is completely dissipated.

2. The source of sublimed material of claim 1 wherein the wall of said body of material to be sublimated is of generally uniform thickness, and said inner surface configuration and the configuration of said heat source are correlated to provide a generally uniform rate of total heat energy absorption at substantially all portions of said body with a consequent uniform sublimation rate over substantially all portions of the outer surface of said body.

3. The source of sublimed material of claim 1 wherein said inner surface of said body includes a portion which is rougher than other portions to increase absorption of heat at said roughened portion.

4. The source of sublimed material of claim 3 wherein means acting as a heat sink is in heat conducting relationship to said body adjacent said roughened inner surface portion, and said roughened portion increases said heat absorption of said portion to compensate for heat loss due to the presence of said heat sink.

5. The source of sublimed material of claim 4 wherein said means acting as a heat sink is a support member secured to said body for mounting the same in a vacuum chamber.

6. The source of sublimed material of claim 1 wherein substantially all of said inner surface of said body is curved generally concavely with respect to said source of heat energy to provide said reflection of heat energy from any one portion of said surface to another portion of said surface for absorption by said material to be sublimated.

7. The source of sublimed material ofclaim 6 wherein said inner surface configuration is generally spherical.

8. The source of sublimed material of claim 7 wherein said source of heat energy is an open, generally cylindrical radiating body.

9. The source of sublimed material of claim 7 wherein the outer surface of said body also has a configuration which is generally spherical and the wall thickness of said hollow body is generally uniform over its full extent, and the configuration of said heat source is correlated to said spherical inner surface to provide a generally uniform rate of total heat energy absorption at substantially all portions of said body and a consequent uniform sublimation rate over substantially all portions of the outer surface of said body.

10. The source of sublimed material of claim 9 wherein said body includes a relatively short tubular section joining two hemispherical sections at the midplane thereof to provide said generally spherical inner and outer surfaces.

11. A source of sublimed material for high vacuum pumping comprising a body of a material to be sublimated having a wall defining two opposite surfaces, a first surface for receiving heat energy and a second one for the sublimation of material therefrom due to the conduction of heat through said body from said first surface, and a source of heat energy for directing heat energy at said first surface, said first surface including a portion which is rougher than other portions to increase absorption of heat at said roughened portion for conduction through said body.

12. The source of sublimed material of claim 11 wherein means acting as a heat sink is in heat conducting relationship to said body adjacent said surface portion, and said roughened portion increases said heat absorption at said portion relative to the remainder of said surface to compensate for heat loss adjacent said portion due to the presence of said heat sink.

13. The source of sublimed material of claim 12 wherein said means acting as a heat sink in a support member secured to said body for mounting the same in a vacuum chamber, said body is hollow, and said source of heat energy is positioned inside said body.

14. A source for providing sublimed material comprising an electrical heater, a wall made of said material to be sublimed, said wall having inner and outer surfaces and being shaped to provide a hollow body substantially enclosing said heater, said heater being spaced from contact with said inner surface of said wall, said wall having an aperture therein, a lead for said heater passing through said aperture, and said heater within said hollow body having a size substantially larger than said aperture.

15. The source of sublimed material of claim 14 wherein said inner surface of said wall is entirely concave.

16. The source of sublimed material of claim 14 further comprising a support structure connected to said hollow body, an electrical connector attached to said heater lead, and said support structure being mechanically connected to said electrical connector by an electrical insulator.

17. The source of sublimed material of claim 16 wherein said heater has a second lead, said hollow body has a second aperture, an electrically conducting plug is positioned in said second aperture in electrical contact with the wall of the aperture, said second lead is electrically connected to said plug, and said plug is of a material having a sublimation temperature below that of said wall.

18. The source of sublimed material of claim 16 wherein said inner surface of the wall adjacent the connection of said support structure to said hollow body is rough compared to other portions of said inner surface.

* IIK 

1. A source for providing sublimed material comprising a hollow body of a material to be sublimed, said hollow body having inner and outer surfaces, a source of heat energy located within said hollow body for directing heat energy at the inner surface of said hollow body for conduction through said body to sublime said material from said body''s outer surface, said hollow body being substantially closed to prevent escape therefrom of both the heat energy flowing directly from said source and the heat energy reflected from said inner surface of said body, the inner surface of said body having a configuration such that heat energy reflected from any one portion of said surface is ultimately directed to another portion of said surface for absorption by said material to be sublimated, said inner surface configuration and the configuration of said heat source being related to correlate the rate of total heat energy absorption at each portion of said body with the wall thickness at said portion so that substantially all of the material of said portion is sublimed at the end of a predetermined time interval which is generally the same for all portions of said body, whereby all portions of said body are substantially dissipated at the end of said interval to maximize the amount of material which is already sublimated from said body at the time at which any portion of said body is completely dissipated.
 2. The source of sublimed material of claim 1 wherein the wall of said body of material to be sublimated is of generally uniform thickness, and said inner surface configuration and the configuration of said heat source are correlated to provide a generally uniform rate of total heat energy absorption at substantially all portions of said body with a consequent uniform sublimation rate over substantially all portions of the outer surface of said body.
 3. The source of sublimed material of claim 1 wherein said inner surface of said body includes a portion which is rougher than other portions to increase absorption of heat at said roughened portion.
 4. The source of sublimed material of claim 3 wherein means acting as a heat sink is in heat conducting relationship to said body adjacent said roughened inner surface portion, and said roughened portion increases said heat absorption of said portion to compensate for heat loss due to the presence of said heat sink.
 5. The source of sublimed material of claim 4 wherein said means acting as a heat sink is a support member secured to said body for mounting the same in a vacuum chamber.
 6. The source of sublimed material of claim 1 wherein substantially all of said inner surface of said body is curved generally concavely with respect to said source of heat energy to provide said reflection of heat energy from any one portion of said surface to another portion of said surface for absorption by said material to be sublimated.
 7. The source of sublimed material of claim 6 wherein said inner surface configuration is generally spherical.
 8. The source of sublimed material of claim 7 wherein said source of heat energy is an open, generally cylindrical radiating body.
 9. The source of sublimed material of claim 7 wherein the outer surface of said body also has a configuration which is generally spherical and the wall thickness of said hollow body is generally uniform over its full extent, and the configuration of said heat source is correlated to said spherical inner surface to provide a generally uniform rate of total heat energy absorption at substantially all portions of said bodY and a consequent uniform sublimation rate over substantially all portions of the outer surface of said body.
 10. The source of sublimed material of claim 9 wherein said body includes a relatively short tubular section joining two hemispherical sections at the midplane thereof to provide said generally spherical inner and outer surfaces.
 11. A source of sublimed material for high vacuum pumping comprising a body of a material to be sublimated having a wall defining two opposite surfaces, a first surface for receiving heat energy and a second one for the sublimation of material therefrom due to the conduction of heat through said body from said first surface, and a source of heat energy for directing heat energy at said first surface, said first surface including a portion which is rougher than other portions to increase absorption of heat at said roughened portion for conduction through said body.
 12. The source of sublimed material of claim 11 wherein means acting as a heat sink is in heat conducting relationship to said body adjacent said surface portion, and said roughened portion increases said heat absorption at said portion relative to the remainder of said surface to compensate for heat loss adjacent said portion due to the presence of said heat sink.
 13. The source of sublimed material of claim 12 wherein said means acting as a heat sink in a support member secured to said body for mounting the same in a vacuum chamber, said body is hollow, and said source of heat energy is positioned inside said body.
 14. A source for providing sublimed material comprising an electrical heater, a wall made of said material to be sublimed, said wall having inner and outer surfaces and being shaped to provide a hollow body substantially enclosing said heater, said heater being spaced from contact with said inner surface of said wall, said wall having an aperture therein, a lead for said heater passing through said aperture, and said heater within said hollow body having a size substantially larger than said aperture.
 15. The source of sublimed material of claim 14 wherein said inner surface of said wall is entirely concave.
 16. The source of sublimed material of claim 14 further comprising a support structure connected to said hollow body, an electrical connector attached to said heater lead, and said support structure being mechanically connected to said electrical connector by an electrical insulator.
 17. The source of sublimed material of claim 16 wherein said heater has a second lead, said hollow body has a second aperture, an electrically conducting plug is positioned in said second aperture in electrical contact with the wall of the aperture, said second lead is electrically connected to said plug, and said plug is of a material having a sublimation temperature below that of said wall.
 18. The source of sublimed material of claim 16 wherein said inner surface of the wall adjacent the connection of said support structure to said hollow body is rough compared to other portions of said inner surface. 